<template>
    <ul class="list">
        <li class="item" :ref="item" v-for="item of letters" :key="item" @click="handleLetterClick" @touchstart="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd">
          {{item}}
        </li>
    </ul>
</template>
<script>
export default {
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
      // 数据截流，控制函数执行的频率
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handleLetterClick (e) {
      // console.log(e.target.innerText)
      this.$emit('change', e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          // const startY = this.$refs['A'][0].offsetTop
          // console.log(startY)
          const touchY = e.touches[0].clientY - 74
          const index = Math.floor((touchY - this.startY) / 23)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>
<style lang="stylus" scoped>
@import '~styles/variable.styl'
    .list
      display flex
      flex-direction column
      justify-content center
      position absolute
      top 1.58rem
      right 0
      bottom 0
      width .4rem
      .item
        text-align center
        line-height .44rem
        color $bgColor
</style>
